Light amplifier



July 29, 1952 l. A. GREENWOOD, JR., TAL 2,605,335

LIGHT AMPLIFIER Filed May 25. 1949 Patented July 29, 1952 Nr oFFIcE LIGHT AMPLIFmnf Ivan'AlfGreen'who d`,"5J1- Pleasantvillle, and Everett` Bi'Hales; MountKisco, N. Yi, ras'sign'ors toY Gen'- eral vPrecision vLaboratory Incorporated, afcorporation-of NewLYork `Appintan-lim.May 25, 1949,'seria1fNd; 95,2452,

, 1- Thisinven'tion relates to a ,light 'amplier having a wide range of 'utility andone Whichis' particularly suitable for 'use in' projectionltelevision systems' wherein the' received television image is projected" onY av relatively large screen'.

Irproje'ctiontelevisionsystems in common'use the received images 'are displayed on the faceV of a small cathode 'ray tube bymeans'well known in the 'art and these images are inturn'projected' on a screen by means of any'one of a number of projectionsystems; Allof 'thesesyst'ems merely` enlarge the image`r formed on lthe cathode ray tube fluorescent *screen to' a size'suit'able` vfor `display onthe Viewing screen and hence'theamount of lightper unit of surface `ofthe viewing screen is-v correspondingly" decreased'. 'Thisv results in relatively'poor'illumination of the viewingscreen asth'ere 'is 'alimit tothej amount of light which mayA be produced at'the fluorescent'screenY "of the cathode ray tube: K

The' instant'invention has-for itspurpose the provisionofa system-wherein at the same time that the picture is-y beingenlarged by lsuitable projection optics the amount of light derived from thecathoderay'tubey screen is also amplied thus 3 rciaima- (C1. Irv- 3118i lOl yielding-anenlarged imagevof a brightness herefaceeand a-largeI accelerating-field isappl'iedbetween-these elements-sov that a Visible imageof the yphoto emissicnisproduced.'

The photo-emissive surfacen andA the second fiuorescent screen'v maybe positioned closely adjacent each'other'imwhich Yeventif `a-'large potentiai diierence exists therebetween Vno focusing eldis necessary.

Likewise the evacuated envelope' containing the photo-emissive" surfaceand fluorescent screenA vmay bemade of such a surfacearea that the" uorescent screen'itselfacts as the'viewing screen, the equipment occupyingno` more 'space than vpresent'projection television systemsbut operating'witha considerably'greater luminous flux ironia given yarea-ofthe screenfj y Alternatively the same` lightamplifier`V system; may be used as an intermediateelementasec" ond'piojection system being provided to project the' light image formed on the light amplier flucrescentscreen on a suitable viewing screen.

In' eitherl arrangement, however, the light is ampliiiedlatthe saine time that the image is enlarged in area so lthat the final image as Viewed by the beholder is more brilliant than has heretofore' been attained in large screen television Fig. 3'y isa diagrammatic illustration vof as fu1' ther embodiment of the invention in which the photo-emission surface-of the light amplier is positioned closely adjacent the yfluorescent screen of the cathode ray tube.

Referring now tov Fig. l a television cathode* ray tube I I operated in the conventional manner: displays Vthe received images on the usual fluorescent screen I2.V Thescreen I2 maybecomparativelyrestricted in areaasrespects the-area desired to be observed by the' viewer. In orderf that appropriate enlargement of the image may be attained; the image' displayed on thescreen I2 is projected throughan'appropriate lens/system-indicated` diagrammatically by they lens I3. and light raysfltl and I6 onto a novel combination of light amplier and viewing scr'een'indicateclV generally' at I l.

The light amplierand vviewing'screen AIl consistsl of'anevacuated chamber I Scompose'd Wholly or partially-oiglass havingtwo faces I9 and 2l off relatively largef'area-sp'aced from" each otherv by asmall amount.- so that the resultant'unit formed thereby-fisA ofV considerable height andwidth by relatively shallow depthiforming'a" unit which-maybe readily fitted intothe surface of a" suitable cabinet containing a television receiver chassis'.

The interior offthefaceV l iscoatedwith a thin layer. 22 ofv photo-emissivematerial, the Alayer.

. being o fv such a depth as to be semi-transparent. Y A real. image of` thev display of the uorescent-A screen" I 2"is pr'ojec'ted'onv thephoto-emissi-velayerf are emitted by the layer 22 the density of which in any elemental area of the layer 22 corresponds to the amount of light impinging thereon.

The opposed face 2| of the chamber I8 is coated with a layer of fluorescent material 23 on which a backing layer 24 of aluminum, silver or the like may be superimposed for purposes as will more fully appeal` hereinafter.

A large accelerating field indicated diagrammatically by the battery 26 provided with adjusting means 21 is connected between the photoemissive surface 22 and the fluorescent screen 23 through the medium of conductors 28. This large accelerating field causes the electrons emitted Yby the photo-emissive surface 22 to pass through the backing layer 24 and impinge on the iiuorescent layer 23 producing a visible light image thereon. Where the distance between the layers 22 and 23 is small, say in the order of a centimeterA or less and a large accelerating potential is impressed therebetween, no focusing such as a magnetic eld is necessary to cause the light image to agree in detail with the electron image producd by the layer 22 since in the short distance between the layer 22 and fluorescentv screen 23 the electrons will travel in substantially straight lines.

The acceleration of the electrons emitted by the photo-emissive layer 22 results in an increased brightness of the image on the uorescent screen 23 of the order of twenty times the brightness that would be attained if the image on the screen I2 were merely enlarged to the size of that depicted on the screen 23. Thus an enlargement of approximately 4.5 diameters may be attained which has the same brilliancy as the original image of reduced size.

Some further gain in light amplification may also be attained by the judicious use of light feedback between the photo-sensitive layer 22 and the fluorescent screen 23.

If the photo-sensitive layer 22 is affected by light of the wavelength given off by the fluorescent screen 23 a regenerative eifect will be produced since the light from the screen 23 falling on the photo-sensitive layer 22 will increase the electron emission thereof which in turn will result in an increased illumination of the screen 23. This regenerative effect while useable to a controlled extent to y'increase the gain in light intensity must not be unlimited in its application as excessive amounts of such regeneration will reduce the contrast of the image depicted on the screen 23 or indeed may be carried to such an extent as to renderl the device uncontrollable.

In order, therefore, that the regenerative effect may be kept within proper limits, thefluorescent screen 23 is coated on its'side adjacentto the photo-sensitive surface 22 with a thin semitransparent layer 24 of aluminum or other metallic material. Thus a fraction only of the' light of the screen 23 is transmitted back to the photosensitive surface 22 and the amount of the'light so reected back may be `controlled by choosing a proper thickness for the layer 24 so that only the desiredamount of regeneration` is obtained.

On the other hand, a phosphor may be chosen for the screen I2 which produces an image mainly in the ultraviolet region and the photo-sensitive surface 22 may be made of such material as to be substantially unaffected by light of longer wavelengths vthan ultraviolet. Thus when a screen 23 is Aused having a phosphor which produces an image mainly of light in the visible'regionslittle if any regeneration eiect will take 4 place because the photo-sensitive layer 22 is unaffected by such light.

In some instances it may be desirable to provide a viewing screen which is separate and distinct from the light amplifying device permitting an amplifier of small physical dimensions. Such anarrangement is disclosed in Fig. 2 in which elements similar tothose of the system of Fig. 1 have been accorded similar reference numerals. Referring to Fig. 2 a television cathode ray tube I I having a fluorescent screen emits a light image either in the visible or ultraviolet range as discussed above and this image is projected on a photo-sensitive surface 22 deposited on one interior face I9 of a light amplifier II. The light amplifier II is similar in all respects to that disclosed and described in connection with Fig. 1 save only in the matter of size, the height and width being smaller than that of the similar amplifier of Fig. 1 since in this instance the uorescent screen 23 of the light amplifier I1 is not also used as the viewing screen.

The function of light amplification, however, is performed in the same manner by the use of similar structure and hence a detailed discussion need not be repeated. Suffice it to say that a light image is formed on the fluorescent screen 23 whose luminous flux for an equivalent area is considerably greater than that of the screen I2 of the cathode ray tube I I.

The light image of increased brightness produced on the screen 23 may thenV be projected on any suitable viewing screen 29 through the medium of a suitable optical system indicated diagrammatically by the lens 3|. The screen 29 may be translucent so that the image projected thereon may be viewed from the side opposite to the light amplifier I1 and cathode ray tube I I or alternatively a screen of high light reecting properties may be utilized permitting the image to be viewed from the same side on which the cathode ray tube II and light amplifier I1 are placed as in the usual projection of slide and` motion pictures.

When the image formed on the fluorescent screen of the light amplier is projected on another screen for enlarged viewing purposes, the light amplifier may be made a part of the cathode ray receiving tube itself obviating the necessity of the interposition of an optical system between the cathode ray tube and the light amplier. Such'a system is depicted in Fig. 3.

Turning now to Fig. 3 a cathode ray tube 35 havingthe usual electron gun assembly and deecting means (not shown) is provided adjacent itslarger end with a fluorescent screen 37 which is formed by coating one surface of a thin transparent member 38 with a layer of suitable fluorescent material. The member 38 is mounted in the enlarged end of the cathode ray tube 36 in any suitable manner and its face opposite that provided with the fluorescent layer is coated with a `layer of photo-sensitive material as indicated at 39. Thus the photo-sensitive surface is closely juxtaposed to the uorescent screen 3l and the light image formed on the screen 3l produces an emission of electrons by the photo-sensitive surface 33, the amount of which Vis proportional in any elemental area to the light intensity of the corresponding area on the screen 31.

This electron image is accelerated by a high potential supplied by the source 4I towards a second fluorescent surface i2 which may be backed by an aluminum'or other metallic layer 43 for the purposes'as set forth above.

`In the same manner as'previously described the electron image so accelerated produces a light image on the screen 42 which is considerably increased in brilliance over that originally produced on the screen 31.

The light image of increased and amplified brightness produced on the fluorescent screen 42 is then projected on a viewing screen 45 of enlarged area by means of any suitable optical system, here diagrammatically illustrated by a single lens 44.

Thus in the present system the image depicted on a television receiving tube is not only enlarged for greater ease in viewing but also the amount of light available at the screen of the receiving tube is amplified so that the resultant enlarged image is comparable in light intensity to the smaller image of the cathode ray receiving tube itself and both an enlarged and brilliant image is attained.

What is claimed is:

1. A light amplier for use in a television receiving system wherein the received light image is projected on a viewing screen comprising, an evacuated container, a photo-sensitive layer having said light image impressed thereon whereby an electron image corresponding thereto is produced, a uorescent screen, means for applying an accelerating potential between said photosensitive layer and said fluorescent screen, said photo-sensitive layer and said fluorescent screen being positioned in said evacuated container in immediate proximity to each other so that the electrons emitted by elemental areas of said photo-sensitive layer impinge on corresponding elemental areas of said fluorescent screen under the sole impetus of said accelerating potential and a semi-transparent metallic layer on the face of said fluorescent screen adjacent said photosensitive layer.

2. A light amplifier comprising, a cathode ray image tube having a fluorescent screen, a photosensitive layer of substantially larger area than said fluorescent screen, means for projecting an enlargement of the image produced on said fluorescent screen on said photo-sensitive layer whereby a corresponding enlarged electron image is produced; a second fluorescent screen of substantially the same area as said photo-sensitive layer positioned closely adjacent thereto, means for applying an accelerating potential between said photo-sensitive layer and said second 11u0- rescent screen and a semi-transparent metallic coating on the face of said second fluorescent screen which is adjacent said photo-sensitive layer.

3. A light amplifier comprising, a cathode ray receiving tube having a fluorescent screen,y a photo-sensitive layer in immediate proximity thereto whereby an electron image corresponding to the light image on said fluorescent screen is produced, a second fluorescent screen positioned closely adjacent said photo-sensitive layer, means for applying an accelerating potential between said photo-sensitive layer and said second uorescent screen, a semi-transparent metallic layer on the face of said second fluorescent screen adjacent said photo-sensitive layer and means for viewing the light image produced on the other face of said second fluorescent screen by the combined action of said electron image and accelerating potential.

IVAN A. GREENWOOD, JR. EVERETT B. HALES.

REFERENCES CITED The following references are of record in the fue lof this patent:

UNITED STATES PATENTS Number Name Date 2,177,360 Busse Oct. 24,- 1939 2,200,749 Kemp May 14, 1940 2,258,294 Lubszynski et al Oct. 7, 1941 2,270,373 Kallmann et al. Jan. 20, 1942 2,297,478 j Kallmann Sept. 29, 1942 

